We report on the first sub-arcsecond (0.44 $times$ 0.41 arcsec$rm ^2$) angular resolution image at 150 MHz of the A-nucleus in the Luminous Infrared Galaxy Arp$,$299, from International Low Frequency Array (LOFAR) Telescope observations. The most remarkable finding is that of an intriguing two-sided, filamentary structure emanating from A-nucleus, which we interpret as an outflow that extends up to at least 14 arcseconds from the A-nucleus in the N-S direction ($approx$ 5 kpc deprojected size) and accounts for almost 40% of the extended emission of the entire galaxy system. We also discuss HST/NICMOS [FeII] 1.64 $rm mu m$ and H$rm_2$ 2.12 $rm mu m$ images of Arp$,$299-A, which show similar features to those unveiled by our 150 MHz LOFAR observations, thus giving string morphological support for the outflow scenario. Finally, we discuss unpublished NaI D spectra that confirm the outflow nature of this structure. From energetic arguments, we rule out the low-luminosity active galactic nucleus in Arp$,$299-A as a driver for the outflow. On the contrary, the powerful, compact starburst in the central regions of Arp$,$299-A provides plenty of mechanical energy to sustain an outflow, and we conclude that the intense supernova (SN) activity in the nuclear region of Arp299-A is driving the observed outflow. We estimate that the starburst wind can support a mass-outflow rate in the range (11-63) $rm M_{odot} yr^{-1}$ at speeds of up to (370 - 890) $rm km , s^{-1}$, and is relatively young, with an estimated kinematic age of (3 - 7) Myr. Those results open an avenue to the use of low-frequency (150 MHz), sub-arcsecond imaging with LOFAR to detect outflows in the central regions of local luminous infrared galaxies.
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